The objectives of the proposed research are to explore the influence of various aspects of the rat pup stimulus complex (contact: tactile, thermal, taste; exteroceptive: sight, sound, smell) on the induction (in virgins), initiation and maintenance (postpartum or post-Caesarian-section delivery) of maternal behavior. The sensory regulation of prolactin secretion in lactating, thelectomized (nipple-removed) postpartum, and virgin mothers will also be assessed. Finally, experiential, social, and maturational influences on maternal responsiveness will be studied. To date we have found that the age of pups influences the likelihood and rapidity of maternal behavior onset in Sprague-Dawley virgins housed with pups continuously. Pups aged 1-2 days are more effective (2 day latency) than pups aged 3-12 days (4.0 to 5.5 day latencies), 13-14 days (7 day latencies), or 15-16 days (full maternal behavior not reliably elicited). In Long-Evans females delivered of their fetuses shortly prior to term, brief daily contact with pups (15 min x 2) or 24 hours of exteroceptive exposure hastened maternal behavior onset 8 days later compared with controls receiving no pup contact after C-section. Ultrasound emissions by pups are being studied as a function of a number of variables, such as age and maternal deprivation, and will be related to the induction and/or maintenance of maternal behavior.